New York City subway commuters trip going up these stairs

In New York, Dean Peterson decided to explore why everyone trips on a certain set of stairs. It turns out that the stair is a fraction of an inch higher than all the rest, sending nearly every stair-climber toppling.

Sometimes changing the rise of one step in a stair to make it slightly higher is deliberate, as in Edinburgh where in one very old house the variation functioned as a very early burglar alarm, causing intruders who were not familiar with the stair to trip and give themselves away.